1. Field of the Invention
This invention relates in general to microelectromechanical systems, also known as MEMS, in which mechanical micro-components are fabricated for use in electronics, for example in flat panel displays employing field-effect display (FED) technology.
2. Description of the Related Art
Electronic displays are rapidly becoming one of the major components in the emerging information highway system. Among the well-known displays are cathode ray tubes, plasma displays, electroluminescent panels and active matrix liquid crystal displays. Flat panel displays have been emerging as replacements for cathode ray tubes in television, computer monitors and other electronic visual displays. Field-effect flat panel displays have been developed which provide large two-dimensional screens with less weight and reduced costs as compared to the large envelopes required for displays such as cathode ray tubes. FEDs also have certain advantages over liquid crystal displays, electroluminescent and plasma displays because the FEDs have greater luminosity, lower power requirements, and are not limited in viewing angle or speed of operation.
The FED technology has advanced to the point of using cold field emission with microfabrication techniques to produce dense arrays of micron-sized cones in silicon dioxide. Microfabrication of sharp points on the cones leads to high fields and short flight distances, resulting in adequate focusing. The use of microfabrication techniques makes it possible to manufacture thousands of the devices simultaneously so that the cost of manufacture is low.
Flat panel displays are placed in large flat vacuum envelopes of which one panel is of a suitable transparent or translucent material such as glass. One surface of the glass panel is coated with a pattern of highly efficient phosphors. Atmospheric pressure will distort or collapse the glass panel unless it is made of thick glass or adequately supported over its surface. For making envelopes sufficiently light in weight, the preferred solution is to place spacers at frequent intervals within the vacuum space to maintain the distance between the front and back surfaces. While certain university research projects have provided experimental displays in which micron-scaled components have been manipulated into position on a substrate surface to support an overlying glass plate, such an arrangement is impractical for large scale, low cost commercial manufacture of FEDs. This is because the size of practical FEDs requires many thousands of the supporting elements distributed over a substrate surface such that it would be impractical to individually manipulate the components into position.
It is also advantageous if the supporting spacer is fabricated as a part of the FED device, a feature which has not been achieved in the prior art. It is required that hundreds or even thousands of the small spacers be accurately machined and strategically placed among the emitters. The spacers must also not interfere with electrical functioning nor impede the evacuation of air. Microfabrication of the spacers must be compatible with other manufacturing operations utilized in fabricating the emitters. In an FED there are narrow spaces or "streets" between emitter pixels so that the spacers, and actuators for the spacers, must be thin and long to fit within those narrow streets.
The need has therefore been recognized for a microelectromechanical fabrication system, method and apparatus which obviates the foregoing and other limitations and disadvantages of the prior art. Despite the various microelectromechanical systems and devices in the prior art, there has heretofore not been provided a suitable and attractive solution to these problems.